The present invention relates to a method of producing a mixture that contains rubber or rubber-like material, and carbon black, including the step of preheating in a high-frequency alternating field.
Since the preheating of rubber in hot air chambers causes problems, it has already been proposed to preheat rubber in a high-frequency alternating field or zone. However, this type of preheating could not be accepted in practice because most types of rubber have a dielectric dissipaion factor that is too low.
Furthermore, at the beginning of a mixing procedure, different time spans are needed for plasticizing and decrystallization as a function of the temperature at which the rubber is introduced into the kneader. In addition, the local nonuniformity of the heating-up of cold rubber balls also facilitates the creation of rubber portions that are overfilled with highly active fillers and that experience has shown can be distributed in the other matrix only with great difficulty, if at all. Furthermore, the time until energy absorption, i.e. the time up to the actual mixing process, is a function of the viscosity and the hardness of the balls that are supplied. This also leads to nonuniformity during the production of the mixture. These problems are particularly prevalent with paddle kneaders having intermeshing paddles; furthermore, these kneaders are more difficult to charge due to their construction.
The present invention furthermore proceeds from the recognition that due to the difficulties connected with the handling of carbon black, it appeared advantageous with emulsion polymers to already add the carbon black in the latex phase in order in this manner to shorten the further mixing time and to preclude the disadvantageous granulation of the carbon black. A similar situation applies to the solution polymers, since in such a situation, due to the low shearing forces, an effective as possible preliminary distribution of the carbon black would result in still greater advantages relative to the mixing. However, the so-called carbon black batch has limitations. This is based, among other things, on the variety of carbon black types, and on the inability to be able to properly screen the carbon black that is used during the fabrication of the rubber products. For these reasons, in practice by far the greatest amount of rubber mixtures are produced without carbon black batch.
It is therefore an object of the present invention to avoid the aforementioned drawbacks. In particular, with the present invention it should be possible during the manufacture of rubber mixtures of various properties, to be able to start to a certain extent from the same mixing conditions, especially from the same starting temperatures, so that consequently, with the existence of a specific batch, it is possible to produce therefrom, for example, all current tread mixtures for vehicle tires, or all adhesive mixtures for the construction of automobile tires. Another object of the present invention is to reduce the overall mixing time.